Sol-gel route to direct formation of silica aerogel microparticles using supercritical solvents

A simple and versatile method to obtain silica aerogel particles based on the hydrolysis and subsequent condensation of silicon alkoxides in supercritical fluids is proposed. This microparticle production route reduces the number of steps of traditional microparticle sol-gel processing. A case example is explained in more detail. Spherical and fiber silica morphologies were obtained by a one step method using a sol-gel process with supercritical acetone as a solvent. Particle size was controlled by varying the relative amounts of alkoxysilane, water and acetone. The resulting materials are influenced by a large number of experimental parameters; it has been observed that a quite relevant one is the supercritical fluid venting rate. The morphology of the particles was characterized by electron microscopy (SEM and TEM) and Atomic Force Microscopy (AFM). Alternatively, a low temperature synthesis can be performed by using supercritical carbon dioxide as solvent and formic acid as condensation agent.